Title: Effect of Habitat Depth on Host Location by Five Species of Parasitoids (Hymenoptera: Pteromalidae, Chalicididae) of House Flies, Musca Domestica L. (Diptera: Muscidae), in Three Types of Substrates

Interpretive Summary: Parasitic wasps are important tools for managing house flies and stable flies on livestock and poultry farms. Wasp releases can reduce fly populations and save farmers money while reducing the amounts of insecticides needed for their fly control programs. Many species of these wasps occur outside the U.S. but there are few objective criteria for determining whether or not to import and release them. This study was part of a larger project to improve our understanding of the relative usefulness of different wasp species in different situations encountered on farms. In this study, conducted at USDA's Center for Medical, Agricultural and Veterinary Entomology (Gainesville, FL), five species of wasps were evaluated for their ability to locate fly pupae at different depths in various substrates. (Fly pupae in the field are found in many habitats and at variable depths). Three of the species were native to the US (Muscidifurax raptor, Spalangia endius, and S. cameroni) and two were exotic species being considered for importation (Dhirinus himalayanus and Spalangia gemina). Two of the species tended to forage near the surface of the substrates (M. raptor and D. himalyanus), whereas the Spalangia species searched at greater depths. None of the species were effective at locating pupae that were buried in sandy soil, indicating that outdoor fly populations in regions of the country with extensive coastal planes such as Florida have a degree of protection from fly parasites. The results also indicated that releases of combinations of M. raptor and one of the Spalangia species should provide better fly control than any single species.

Technical Abstract:
Five species of parasitoids (Muscidifurax raptor Girault and Sanders, Spalangia cameroni Perkins, Spalangia endius Walker, Spalangia gemina Boucek, and Dihrinus himalayanus [Masi]) were evaluated for their ability to locate house fly pupae at various depths in poultry manure (41 degrees moisture), fly rearing medium (43 degrees moisture), and sandy soil (4 degrees moisture) from a dairy farm. In manure, searching activity of all five species was largely confined to the surface (M. raptor, D. himalayanus and S. gemina) or to depths of up to 2 cm below the surface. S. cameroni was the most effective species at locating buried pupae in manure. All of the species searched over a wider range of habitat depths in fly rearing medium, although M. raptor and S. gemina tended to concentrate their searching activity relatively close to the surface of the substrate; host attacks by these species at 6 cm were 30-40 degrees lower than on the surface of the medium. S. endius searched uniformly at all depths in rearing medium and S. cameroni had highest rates of host attacks 1-2 cm below the surface of this substrate. The parasitoids displayed considerable fidelity to their search patterns regardless of whether or not they were given a choice of habitat depths in which they could find pupae. None of the parasitoids were effective at attacking fly pupae that were buried in sandy soil at any depth. The results suggest that fly larvae that pupate in the sandy soils typical of Florida's coastal plane are relatively impervious to attack by pupal parasitoids.